1. Field of the Invention
The present invention relates to a semiconductor device, a liquid crystal display device, and an electronic appliance including them. In particular, the present invention relates to a semiconductor device and a liquid crystal display device in which an electric field generally parallel to a substrate is generated to control liquid crystal molecules, and an electronic appliance including the semiconductor device or the liquid crystal display device.
2. Description of the Related Art
As one of plans for technical development of a liquid crystal display device, to widen a viewing angle can be given. As a technique for realizing a wide viewing angle, a mode in which an electric field generally parallel to a substrate is generated and liquid crystal molecules are moved in a plane parallel to the substrate to control grayscale is employed. As such a mode, IPS (In-Plane Switching) and FFS (Fringe-Field Switching) are given. In these modes, a first electrode (such as a pixel electrode with which voltage is controlled for each pixel) having a slit (an opening pattern) is located under a liquid crystal and a second electrode (such as a common electrode with which common voltage is applied to all pixels) is located under the first electrode. An electric field is applied between the pixel electrode and the common electrode, so that the liquid crystal is controlled. With such layout, an electric field in a direction parallel to a substrate is applied to the liquid crystal. Therefore, the liquid crystal molecules can be controlled with the electric field. That is, the liquid crystal molecules which are aligned parallel to the substrate (so called homogeneous alignment) can be controlled in a direction parallel to the substrate; therefore, viewing angle is increased.
Conventionally, both common electrode and pixel electrode are formed of ITO (indium tin oxide) (Patent Document 1: Japanese Published Patent Application No. 2000-89255 (FIG. 5 and 14th paragraph)).